Add defensive code for now to RenderLayerRepainter to prevent squashing crashes
when removing certain kinds of layers.

BUG=370410

Review URL: https://codereview.chromium.org/270903002

git-svn-id: svn://svn.chromium.org/blink/trunk@173659 bbb929c8-8fbe-4397-9dbb-9b2b20218538